The present invention relates to a method for controlling a concrete sludge water, such as the water used for producing a ready-mixed concrete or a precast concrete, by washing a mixing drum or other container apparatus in which the concrete was mixed or in which it is adhered, the washing involving a retarder-containing sludge water; removing aggregates from the wash sludge water; and reusing the sludge water thus obtained as part of a mixing water for a fresh batch of concrete, on the next day or after the next day, without discharging waste from the concrete plant. The invention permits detection of excessive or insufficient retarder amounts added to the sludge water, and allows operators to cope instantly with these circumstances.
As taught in the prior art, Japanese Patent Publication (Kokai) No. Hei 2-263100/1990 (Patent No. 265137), it is known to wash a mixing apparatus (in which the concrete adheres) with a retarder-containing water, separating aggregates from the wash water, storing the sludge water thus obtained in a manner so as to retain the activity of the concrete therein, and reusing the sludge water in mixing water for a fresh batch of concrete on or after the next day of operations. No less than 200 concrete plants currently employ this method and consequently ceased discharging deactivated concrete wastes. As the generation of concrete-polluted water has ceased, there has been environmental advantages and the conservation of resources.
Still, concrete plants involve many open-air operations, and the water content, aggregates, and other constituents of concrete can vary from day-to-day. Sand and gravel are natural materials used in concrete, and their compositions may vary. Although concrete is an industrial product, there are variations in the components due to variations in the practices and materials of each manufacturer, the equipment of the concrete plant, and other factors. Accordingly, the accurate control of concrete is difficult. Various types of concrete admixtures have been developed, and concrete is produced according to the specification of a construction company and transported by an agitator vehicle to the construction site by skilled technologists who are needed for sufficient product control.
In addition, the amount of a retarder to be added is not fixed and may vary greatly due to the changes in the seasons. For example, if the day after a mixing and pouring is a holiday, a retarder will be added in a large quantity. Also, the concentration of solids can also greatly affect the amount of retarder in the sludge water. Thus, maintaining control over the amount of retarder added into the concrete at the plant has been rather difficult.
Adding to these difficulties is the fact that dispensers, which supply retarder materials from tanks, are located in open air and sometimes broken down by the effects of wind and rain, and particularly by thunderstorms. Another factor to consider is that many plants are unattended at night. Of course, there is also the possibility of simple mistakes due to operator error, which necessitates double and triple checking. Thus, it is not surprising sometimes to find that retarders are sometimes dosed in amounts two to six times greater than actually required. Concretes prepared with sludge waters containing such large amounts of retarder do not advance operations at the construction site due to the variable and often extended retarding of setting, and this is the trouble that frequently arise where concrete plants are concerned.
Another problem is that if the retarder amount is deficient, the concrete will have lost some of its activity, and when mixed with fresh concrete it will be difficult to mix, and this can result in a concrete mix that is naturally deteriorated. In order to retain quality, the provider of the concrete sometimes disposes of the concrete, an action which is contrary to the purpose of using retarder technology in the first place.
Control over the accuracy in the dosing of retarders is an essential matter for concrete plant operations, but this is far from perfect because the number of highly qualified technologists stationed at concrete plants is sometimes not adequate.